A simple pop power amplifier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

 Comments on the article

The described amplifier is designed for two-channel power amplification of the signal supplied from the mixing console or pre-amplifier. Each of the two inputs has an input level control that allows you to set the required sensitivity. With a switch, you can combine its inputs, while one of the two input connectors can be used as a line output to increase the number of amplifiers working in parallel. The features of the UMZCH include a switchable damping factor for loudspeakers to optimize their sound in various acoustic conditions.

Main Specifications

• Rated input voltage, V......1,1
• Rated output power of each of the two channels, W, at Kg = 1% and load resistance 4 Ohm......400
• 8 Ohm......220
• Operating frequency range, Hz, with unevenness -0,5 dB......20...20000
• Output signal slew rate, V/µs......25
• The coefficient of harmonic distortion of the signal with a level of 1 dB,%, not more than at a frequency of 1 kHz......0,01
• in the operating frequency range ..... 0,1
• Signal-to-noise ratio + background, dB......96
• Maximum permissible deviation of voltage in the network, V......170...270
• Minimum load resistance. Ohm......2.5
• Overall dimensions, mm ...... 430x90x482
• Weight, kg, not more than ...... 16

The amplifier has indicators for the output signal level and its limitation, output overload, as well as indicators for emergency shutdown of loudspeakers and overvoltage of the network.

On fig. 1 shows a diagram of the right channel of the amplifier and the load protection unit.

(click to enlarge)

At the input of the UMZCH, the OU KR544UD2A is used. and circuits C4R4 and R1C3 limit the band of amplified frequencies. They reduce the penetration of infra- and ultrasonic frequencies into the PA, which can lead to an overload of the amplifier and dynamic heads. The voltage amplifier on VT1 - VT4 is similar to that used in [1, 2]. The output of the op-amp is connected to an emitter follower VT3, which, together with the R6C15 circuit, performs the functions of a voltage-to-current converter. This current flows through the cascade from the OB to VT2 to the voltage amplifier on VT1.

Further, the structure of the amplifier is almost symmetrical: the load of the transistor VT1 is the current generator on VT4, the input circuit of the subsequent stage of current amplifiers, as well as the resistor R12, which stabilizes the load resistance for VT1. This is done in order to somewhat reduce the overall gain and increase the stability of the amplifier with a closed feedback loop. The subsequent current amplifier is made in three stages: VT5, VT10. further - VT11, VT17 and then VT12 - VT16, VT18 - VT22 (each arm has five transistors connected in parallel).

The short circuit protection unit (SC) in the load is made on transistors VT6, VT7 and VT8. VT9. connected according to the thyristor analog circuit, for the upper and lower arms, respectively. In the off state, this node has no effect on the output stage. When conditions arise for the protection to operate, the transistors of the corresponding arm of the output stage are completely closed. Thus, the current consumption of the PA during a short circuit and the rated input voltage will be even less than in the idle mode, therefore, in the event of a short circuit at the output, the power amplifier does not fail.

Resistor R14 is necessary for the correct operation of the short circuit protection. For example, when the upper arm is overloaded, the VT6 transistors open. VT7 and the residual voltage at the base of VT5 relative to the output does not exceed 0.8 V. If this resistor is not present, then the bias voltage on the diodes (approximately 2,6 V) will increase the bias voltage for the lower arm of the output stage and unlock it.

Unlike other protection devices with turning off the output transistors [2, 3], the proposed node automatically returns to its original state when the load with a resistance of 2,5 ... 16 Ohm is restored and a useful signal with a level of 25% of the nominal and higher is applied to the amplifier input . Circuits R18C13 and R19C14 eliminate the possibility of false protection operation due to phase shift of the current in the load due to its reactive nature.

In the output stage, the transistors of the final stage operate in the AB mode with a quiescent current of about 100 mA, determined by the bias voltage on the diodes VD9-VD12 and resistors R24, R35. Their relatively small resistance allows this stage to operate in the small signal mode directly to the load and reduces the discharge time of the capacitance of the CBE transistors of the final stage, reducing its switching distortions. These transistors operate in mode B, so they do not require thermal compensation circuits and quiescent current regulation.

The indicator of limiting the output signal and short circuit at the output is powered by negative polarity pulses at the output of the op-amp DA1, which occur as a result of the OS loop breaking when the output signal is limited or the protection unit is triggered.

The device for delaying the connection of the load and its disconnection when a constant voltage appears at the output of the amplifiers is made common for both channels. When the power is turned on, the capacitor C19 is charged through the resistor R49. providing a delay in opening transistors VT25, VT27 and turning on relay K1 for 2 s. When a constant voltage appears at the output of one of the amplifiers, with a positive polarity, the transistor VT23 will open, and in the case of a negative polarity, VT24 will open, locking the transistors VT25, VT27 and turning off the relay.

The loudspeakers are turned off by the protection unit and when the voltage in the network rises above 250 V (VT26. VD17-VT19. R51-R53). As practice shows, the supply voltage is exceeded much more often than one might expect. With an increase in the supply voltage of the protection unit, the current flowing through the zener diodes VD17-VD19 opens the VT26 transistor, as a result, the mains overvoltage indication turns on and the VT23 transistor opens, which leads to a load disconnection. Continuation of work is possible after switching the mains voltage switch to the "250 V" position.

The diagram of the power supply, indication unit and interconnections of both channels is shown in fig. 2.

(click to enlarge)

The numbering of the interconnections of the UM board and the AC protection, as well as the indicator board, corresponds to the numbering of the terminals of the pads on the corresponding drawings of the placement of elements on the printed circuit boards. Each of the two amplifier inputs has an input signal level control (variable resistors R1, R2) that allows you to set the required sensitivity. Pushbutton switch SB1 can combine its inputs.

In UMZCH it is possible to switch the degree of damping of loudspeakers used in different acoustic conditions. When the amplifier is switched to the high output impedance mode (button of the switch SB2 "Out. N / V" is pressed), the output impedance of the amplifier rises to 8 ... 10 Ohms due to the introduction of current feedback from the resistors R3, R4 in the amplifier. This. as practice shows, - the optimal value for most loudspeakers. However, it is easy to change it in any direction by selecting the resistor R2 on the amplifier board.

Note that the mode of increased output resistance significantly increases the reliability of the speakers. The fact is that an increase in the output impedance of the amplifier helps to reduce active losses in the loudspeaker, which makes it possible to use its capabilities more fully and, in addition, significantly reduce intermodulation distortion [4]. The high output impedance mode also reduces the phase shift of the current in the output stage relative to the input signal.

The amplifier is equipped with operation mode control indicators. These are indicators for power on (HL9), emergency shutdown of loudspeakers (HL7) and indicator HL8. indicating a forced shutdown of the load due to a dangerous excess of the supply voltage. Signal level indicators HL2 and HL3. HL5 and HL6 have threshold values ​​of 5, 20 dB, and also show its limitation (LEDs HL1, HL4) for each channel separately. In addition to limiting, the same indicators signal a short circuit at the output of a channel (if the other level indicators are not lit).

The amplifier power supply is simplified as much as possible. The UMZCH itself is powered from a rectifier with a voltage of 70 V; for the protection and indication unit, its own rectifier is used, connected to a separate winding of the power transformer. Fans Ml, M2 are designed for blowing heat sinks of powerful transistors.

Apparently, the purpose of the SB5 switch also requires explanation: in the sound amplification system, it is set to a position in which the minimum noise from mains interference is achieved.

Construction and details

The appearance of the amplifier is shown in fig. 3 (from the rear panel).

Its main components are placed on a metal chassis with a lid. On the front panel with slotted holes there are fans for forced airflow of heat sinks of powerful amplifier transistors, as well as an operating mode indication board. The rear panel has connectors for connecting signal cables and a three-wire power cable, switches for the mains voltage limit and loudspeaker damping factor, and a fuse holder.

Literature

1. Kletsov V. LF amplifier with low distortion. - Radio, 1983. No. 7. p. 51-53.
2. Sukhov N. UMZCH high fidelity. - Radio. 1989. No. 6. p. 55 - 57.
3. Zuev P. Amplifier with multi-loop feedback. - Radio. 1984. No. 11. p. 29-32.
4. Ageev S. Should the UMZCH have a low output impedance? - Radio. 1997, no. 4, p. 14-16.

Author: S.Sakevich, Lugansk, Ukraine

See other articles Section Transistor power amplifiers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive The car will predict the traffic situation 28.01.2014 American automaker Ford Motor has announced a collaboration with specialists from the Massachusetts Institute of Technology and Stanford University in the development of unmanned vehicle control technologies. Scientists will create algorithms with the help of which cars will be able to independently navigate in space. At the end of 2013, Ford announced an autonomous version of the Fusion Hybrid, which is capable of driving on the roads without the participation of a driver. The car is equipped with circular video cameras, laser radars and various sensors that scan the traffic situation, and the on-board computer builds a three-dimensional map of space based on this information and, using special algorithms developed at the University of Michigan, controls the movement of the car in a specific situation. MIT employees are tasked with creating road prediction technologies that will predict the behavior of people and cars in order to avoid collisions with them. It is assumed that robotic vehicles will be able to “see” in advance the sudden appearance of a pedestrian on the roadway or the passage of a car at an intersection at a red traffic light. Stanford engineers are also working on technologies that can expand the view of the road when it is blocked by large objects, such as a truck. On narrow roads, when driving behind a truck or bus, drivers often drive into oncoming traffic to assess the situation ahead and overtake. Sometimes such “peeping” is very dangerous, but with the help of cameras, sensors and a “smart” computer, according to the developers, such maneuvers can be secured. Earlier, Auto.CNews talked about a virtual windshield that allows you to literally see "through" the cars ahead. The system, called the See-Through System, involves the use of special car DVRs and high-speed image volume. The development of unmanned vehicle control systems or some of its functions at Ford is carried out as part of the Blueprint for Mobility project, launched in 2012 to predict the development of the transport system in the near future. The automaker promises to have self-driving cars on public roads by 2025, which is later than some competitors. For example, Audi, BMW and General Motors have announced plans to begin production of self-driving cars by 2020. Tesla, a premium electric car manufacturer, expects to introduce a civilian self-driving car in two years, but specifies that driver intervention will still be required at first.

Other interesting news:

▪ Electric glue

▪ Earth is running out of phosphorus

▪ transparent solar cell

▪ Microwaves for drugs

▪ Mercedes will make trucks more economical

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Intercoms. Article selection

▪ article Can't see the forest for the trees. Popular expression

▪ article Where is it colder - at the North or at the South Pole? Detailed answer

▪ article Burns. Health care

▪ article A simple electronic ballast based on the IR2153 chip. Encyclopedia of radio electronics and electrical engineering

▪ article Knife can be at the top. physical experiment

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024